First-Principles Study on the Gilbert Damping Constants of Transition Metal Alloys, Fe-Ni and Fe-Pt Systems

We adapt the tight-binding linear muffin-tin orbital (TB-LMTO) method to the torque-correlation model for the Gilbert damping constant alpha and perform the first-principles calculation for disordered transition metal alloys, Fe-Ni and Fe-Pt systems, within the framework of the CPA. Quantitatively, the calculated alpha values are about one-half of the experimental values, whereas the variations in the Fermi level dependence of alpha are much larger than these discrepancies. As expected, we confirm in the (Fe-Ni)(1-X)Pt-X and FePt systems that Pt atoms certainly enhance alpha owing to their large spin-orbit coupling. For the disordered alloys, we find that alpha decreases with increasing chemical degree of order in a wide range.